1. Field of the Invention
This invention relates to a light beam scanning apparatus for scanning a light beam by use of a rotating polygon mirror. This invention particularly relates to a light beam scanning apparatus which eliminates adverse effects of jitter caused by rotation nonuniformity of the rotating polygon mirror or the like.
2. Description of the Prior Art
Light beam scanning apparatuses wherein a light beam is deflected and scanned by a light deflector in a main scanning direction on a scanning surface, and at the same time the scanning surface is moved with respect to the light beam in a sub-scanning direction approximately normal to the main scanning direction, have heretofore been widely used, for example, in scanning recording apparatuses and scanning read-out apparatuses. In the light beam scanning apparatuses, a rotating polygon mirror is employed in many cases as the light deflector. The rotating polygon mirror is advantageous from the viewpoint of scanning stability over other light deflectors such as a galvanometer mirror.
However, with the rotating polygon mirror, rotation nonuniformity is often caused by eccentricity with respect to a motor shaft or the like and, as a result, jitter (i.e. fluctuations in the scanning speed of the light beam along a time base) arises on the scanning surface. Besides the rotation nonuniformity, differences in finishing accuracy between the mirror surfaces of the rotating polygon mirror also cause jitter.
When jitter arises, read-out image signals obtained by scanning with the light beam or an image recorded by scanning with the light beam involves jitter components, and the image read-out accuracy or the image recording accuracy is deteriorated.